The unfolded iPhone Duo can tilt on some upright MagSafe stands, according to a demonstration from Arun Maini, who posts as Mrwhosetheboss.
The cause is weight and magnet placement. The MagSafe ring on the back of the Duo sits on only one half. When the phone is open, extra weight hangs off to one side, and some chargers don't have magnets strong enough to hold it up. iPhones also carry an anti-rotation magnet at the bottom of the ring, but some chargers aren't designed to use it. Maini posted his clip on October 21 with a caption asking whether the tilt counts as auto rotate.
The problem may not be universal. Reddit users pointed to a demonstration by Nilay Patel of The Verge, who charged the Duo horizontally on a MagSafe charger with no issue. That is a different setup from an upright stand, so the two demonstrations don't test the same thing.
Practical advice follows from that. Charging the open Duo in portrait orientation likely works, but the safest way to use an upright stand is with the phone closed. A flat charger doesn't have the same rotation issue.
The quirk exposes an old assumption in MagSafe design: a single rigid slab with a ring in the middle, held in place by magnets alone. A foldable with the ring on one half breaks that assumption. A flat pad sidesteps the issue because the desk carries the weight instead of the magnets. Upright stands will likely need a wider base or a ledge under the open phone, and until stands like that exist, anyone planning to keep a Duo on a desk should expect positioning limits with some MagSafe chargers.